Pressure sensitive adhesive composition for optical members, pressure sensitive adhesive layer for optical members, pressure sensitive adhesive optical member and image display

ABSTRACT

Provided are a pressure sensitive adhesive composition for optical members and a pressure sensitive adhesive composition for optical members. The pressure sensitive adhesive composition for optical members according to the present invention comprises 100 parts by weight of an acrylic polymer (A) having a weight-average molecular weight of 500,000 or more, containing at least 50 wt % alkyl (meth)acrylate having an alkyl group with 5 or more carbon atoms and 0.2 to 2 wt % unsaturated carboxylic acid as the monomer unit, 0.1 to 4 parts by weight of an acrylic polymer (B) having a weight-average molecular weight of 2,000 to 50,000, containing at least 70 wt % alkyl (meth)acrylate and 1 to 7 wt % unsaturated carboxylic acid as the monomer unit and having a higher carboxylic acid equivalent than that of the acrylic polymer (A), 0.01 to 1 part by weight of a silane coupling agent, and a crosslinking agent.

CROSS-REFERENCE TO PRIORITY APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/913,992, filed Aug. 6, 2004, which claims priority toJapanese Patent Application No. 2003-34506, filed Oct. 2, 2003. Thedisclosures of each of the above-referenced applications areincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a pressure sensitive adhesivecomposition for optical members. The present invention also relates to apressure sensitive adhesive layer for optical members, which is formedfrom the pressure sensitive adhesive composition for optical members.Further, the present invention relates to a pressure sensitive adhesiveoptical member having the pressure sensitive adhesive layer and also toan image display such as a liquid crystal display, an organic EL displayand PDP, using the pressure sensitive adhesive optical member. Theoptical member includes a polarizing plate, a retardation plate, anoptical compensating film, a brightness enhancement film, and a laminatethereof.

BACKGROUND ART

Optical members used in liquid crystal displays, for example apolarizing plate and a retardation plate, are attached via a pressuresensitive adhesive to liquid crystal cells. Materials used in suchoptical members expand and contract significantly under heatingconditions and moistening conditions so that under such conditions, dryspots and lifting easily occur after attachment. Accordingly, thepressure sensitive adhesive for optical members is required to bedurable even under heating conditions and moistening conditions.

When an attachment surface upon attaching an optical member is bittenwith foreign matter, or an optical member is out of position because oferroneous attachment, the optical member is released for reutilizationfrom a liquid crystal cell. When the optical member is released from thecrystal cell, the re-releasability of the pressure sensitive adhesive toeasily release the optical member is required so as to prevent a gap ofthe liquid crystal cell from being changed or the liquid crystal cellfrom being broken. However, when techniques of merely improving theadhesion state of the optical member are adopted for the reason thedurability of the pressure sensitive adhesive for optical members isregarded as important, the pressure sensitive adhesive is renderedinferior in re-releasability.

Further, the pressure sensitive adhesive for optical member is requiredto uniformly relax stress caused by a dimensional change in opticalmembers such as a polarizing plate under heating or moisteningconditions. When the pressure sensitive adhesive is inferior inrelaxation of stress, residual stress remains in the optical memberssuch as a polarizing plate, to bring about adverse influences such asdiscoloration and coloring failure in some cases.

Various kinds of materials are proposed as the pressure sensitiveadhesive used in optical members. For example, it is attempted toimprove the stress relaxation of the pressure sensitive adhesive byblending a low-molecular weight polymer with a high-molecular weightpolymer (see JP-A 10-279907, JP-A 2000-109771, JP-A 2000-89731, JP-A2001-335767, and JP-A 2002-121521).

JP-A 10-279907 proposes a pressure sensitive adhesive composition havinga crosslinked structure formed by blending 20 to 200 parts by weight ofa low-molecular weight polymer having a weight-average molecular weightof 30,000 or less with 100 parts by weight of a high-molecular weightpolymer having a high functional group proportion. It is disclosedtherein that a three-dimensional structure of the high-molecular weightcomponent in the pressure sensitive adhesive composition preventsfoaming and peeling under high temperature and high humidity, andinternal stress caused by a dimensional change in a polarizing plate canbe absorbed by the low-molecular weight polymer component.

JP-A 2000-109771 proposes a pressure sensitive adhesive compositioncomprising a high-molecular weight polymer blended with a low-molecularweight polymer having a weight-average molecular weight of 500,000 orless. It is disclosed therein that the pressure sensitive adhesivecomposition can relax stress concentration to prevent coloring failureand discoloration of a liquid crystal cell, and after released, does notpermit any residual adhesive or fogging on the liquid crystal cell.

JP-A 2000-89731 proposes a pressure sensitive adhesive compositioncomprising 1 to 50 parts by weight of a low-molecular weight polymerhaving a weight-average molecular weight of not less than 5,000 and lessthan 500,000 blended with 100 parts by weight of a high-molecular weightpolymer, wherein either of the high-molecular weight polymer or thelow-molecular weight polymer contains nitrogen-containing functionalgroups. It is disclosed therein that the pressure sensitive adhesivecomposition is excellent in durability due to binding of thenitrogen-containing functional groups to an adherent, and preventscoloring failure by coping with expansion and contraction of apolarizing plate.

JP-A 2001-335767 proposes a pressure sensitive adhesive compositioncomprising 5 to 100 parts by weight of an acrylic oligomer having aweight-average molecular weight of 1,000 to 10,000 and a bifunctionalcrosslinking agent blended with 100 parts by weight of a high-molecularweight polymer. It is disclosed therein that the pressure sensitiveadhesive composition is excellent in adhesion to an adherent andpossesses excellent relaxation of stress, to attain durability andprevent coloring failure.

JP-A 2002-121521 proposes a pressure sensitive adhesive compositioncomprising 10 to 100 parts by weight of a low-molecular weight polymerhaving a glass transition point of 0 to −80° C. and a weight-averagemolecular weight of 30,000 to 100,000 and a multifunctional compoundblended with 100 parts by weight of a high-molecular weight polymer. Itis disclosed therein that the pressure sensitive adhesive compositioncan cope with peeling, foaming and coloring failure phenomenon, and isexcellent in reworkability (re-releasability) concerned with the degreeof difficulty in releasing a polarizing film from a liquid crystal celland in re-attaching it.

Any of the above pressure sensitive adhesive compositions comprising alow-molecular weight polymer blended with a high-molecular weightpolymer are excellent in durability and absorb internal stress by thelow-molecular weight component. However, it cannot be said that any ofthe above pressure sensitive adhesive compositions sufficiently satisfydurability, re-releasability and stress relaxation. Particularly, thepressure sensitive adhesive compositions are poor in the ability tore-release optical members in order to re-utilize liquid crystal cells.In evaluation of reworkability (re-releasability) in JP-A 2002-121521,reworkability are assumed to be excellent when a pressure sensitiveadhesive polarizing film previously attached to a glass plate, treatedin an autoclave and left at 23° C. under 65% RH for 24 hours shows anadhesion of not higher than 1200 g/25 mm (about 12 N/25 mm) upon peelingat 180°. According to this standard of reworkability, the reworkabilityof a larger crystal cell as an evaluation sample (sample width: 250 mm)are assumed to be excellent when the adhesion thereof upon peeling isnot higher than 12 kg/250 mm. Under this standard, however, the gap ofsuch a larger liquid crystal cell is often broken.

On the other hand, liquid crystal displays come to be used in personalcomputers and TV sets, and large liquid crystal displays are recentlyusable, and the number of large liquid crystal displays is rapidlyincreasing. At present, waste materials from the liquid crystal displaysare not so much, but it is estimated that the waste materials arerapidly increased in near future, and the amount of the waste materialsis estimated to reach about 100,000 tons annually. Waste materials fromTFT liquid crystal panels, for example, are composed of 85 wt % glassand 15 wt % polarizing film (resin). The glass is milled and used ase.g. glass cullets for building materials, but the amount of such reusedglass is not so great at present. This is because isolation of glass isdifficult. Accordingly, there is demand for techniques of separatingglass from other components. Methods of recycling used liquid crystaldisplays are disclosed (see JP-A 2000-24613, JP-A 2000-189939 and JP-A2000-84531), but these methods involve heating the liquid crystaldisplays at high temperatures where enormous energy is required, thusbringing about a problem of higher costs. In addition, methods offractionating and recovering materials constituting liquid crystaldisplays to recycle them are also disclosed (JP-A 2002-159955 and JP-A2001-328849). However, methods using special devices or leading togeneration of waste alkali solutions are hardly generally utilizablebecause of problems in costs and waste liquor treatment. Ananti-reflection film provided with an adhesive, which upon disposal, isreadily releasable is disclosed (JP-A 11-209708).

An object of the present invention is to provide a pressure sensitiveadhesive composition for optical members, which is excellent indurability, re-releasability and stress relaxation. Another object ofthe present invention is to provide a pressure sensitive adhesivecomposition for optical members, which hardly increases adhesion afterstorage for a long time and does not leave a residual adhesive on glassupon disposal or repair. A further object of the present invention is toprovide a pressure sensitive adhesive layer for optical members, whichis formed from the pressure sensitive adhesive composition for opticalmembers. A still further object of the present invention is to provide apressure sensitive adhesive optical member having the pressure sensitiveadhesive layer, as well as an image display using the pressure sensitiveadhesive optical member.

DISCLOSURE OF THE INVENTION

The present inventors made extensive study for achieving the objectsdescribed above, and as a result they found that the following pressuresensitive adhesive composition for optical members can achieve theobjects, and the present invention was thereby completed.

That is, the present invention relates to a pressure sensitive adhesivecomposition for optical members, comprising:

100 parts by weight of an acrylic polymer (A) having a weight-averagemolecular weight of 500,000 or more, containing at least 50 wt % alkyl(meth)acrylate having an alkyl group with 5 or more carbon atoms and 0.2to 2 wt % unsaturated carboxylic acid as the monomer unit,

0.1 to 4 parts by weight of an acrylic polymer (B) having aweight-average molecular weight of 2,000 to 50,000, containing at least70 wt % alkyl (meth)acrylate and 1 to 7 wt % unsaturated carboxylic acidas the monomer unit and having a higher carboxylic acid equivalent thanthat of the acrylic polymer (A),

0.01 to 1 part by weight of a silane coupling agent, and a crosslinkingagent.

In the pressure sensitive adhesive composition for optical members, theacrylic polymer (B) is contained in an amount of preferably 0.1 to 2parts by weight, more preferably 0.2 to 1 part by weight, relative to100 parts by weight of the acrylic polymer (A).

In the pressure sensitive adhesive composition for optical members, theacrylic polymer (A) preferably contains a hydroxyl group-containingmonomer as the monomer unit.

In the pressure sensitive adhesive composition for optical members, thecrosslinking agent is contained in an amount of preferably 0.01 to 5parts by weight relative to 100 parts by weight of the acrylic polymer(A).

Further, the present invention relates to a pressure sensitive adhesivelayer for optical members, which is formed by crosslinking theabove-described pressure sensitive adhesive composition for opticalmembers.

In the crosslinked pressure sensitive adhesive layer for opticalmembers, the gel fraction is preferably 35 to 90% by weight.

Furthermore, the present invention relates to pressure sensitiveadhesive optical members comprising the above-described pressuresensitive adhesive layer formed on one side or both sides of opticalmembers.

Finally, the present invention relates to an image display using atleast one of the above-described pressure sensitive adhesive opticalmembers.

EFFECT OF THE INVENTION

The pressure sensitive adhesive composition for optical membersaccording to the present invention comprises a high-molecular weightacrylic polymer (A) containing a specific amount of a monomer unit ofunsaturated carboxylic acid, a low-molecular weight acrylic polymer (B)containing a monomer unit of unsaturated carboxylic acid in a largeramount than in the high-molecular weight acrylic polymer (A), a smallamount of a silane coupling agent, and a crosslinking agent. A pressuresensitive adhesive layer formed from the pressure sensitive adhesivecomposition hardly increases its adhesion to a liquid crystal cell,owing to the effect of the low-molecular weight acrylic polymer (B).Accordingly, the pressure sensitive adhesive layer is excellent inre-releasability, and even if a long time has elapsed in various stepsafter attachment of an optical member to a liquid crystal cell and theoptical member is stored under high-temperature and high-humidityconditions, the optical member can be easily released from the liquidcrystal cell without damaging or polluting the liquid crystal cell. Thatis, when the optical member is erroneously attached to the liquidcrystal cell, or when the liquid crystal cell is disposed or repaired,the optical member can be easily released from the liquid crystal cellwithout any remaining adhesive. Upon attachment to a larger liquidcrystal cell, the optical member is also excellent in re-releasabilityand can be reutilized without damaging the liquid crystal cell. Theabove effect is significant when the acrylic polymer (B) is added in anamount of 0.1 to 2 parts by weight, particularly 0.2 to 1 part byweight, relative to 100 parts by weight of the acrylic polymer (A).

The detailed reason for the effect of the low-molecular weight acrylicpolymer (B) on prevention of increased adhesion to a liquid crystal cellis not revealed, but it is estimated that the low-molecular weightacrylic polymer (B) can, due to its low molecular weight, occur and movein a crosslinked structure of the high-molecular weight acrylic polymer(A) and is more hydrophilic than the high-molecular weight acrylicpolymer (A), and can thus move to the interface between the liquidcrystal cell and the adhesive, to prevent adhesion from increasing.Further, the low-molecular weight acrylic polymer (B) is effective in avery small amount of 0.1 to 4 parts by weight relative to 100 parts byweight of the high-molecular weight acrylic polymer (A), and thusphenomena such as surface pollution are not recognized at all. As amatter of course, the effect of the composition as a whole including thesilane coupling agent and the crosslinking agent is also brought about.

The pressure sensitive adhesive layer formed from the pressure sensitiveadhesive composition of the present invention can be established so asto have a predetermined gel fraction by the crosslinking agent, and evenif a long time has elapsed in various steps after attachment of anoptical member to a liquid crystal cell and the optical member is storedunder high-temperature and high-humidity conditions, the pressuresensitive adhesive composition in an adhesion state is excellent indurability without peeling, dry spots or foaming. Further, thehigh-molecular weight acrylic polymer (A) is based on the acrylatehaving an alkyl group with 5 or more carbon atoms, and is excellent inrelaxation of stress caused by a dimensional change in optical memberssuch as a polarizing plate, thus remaining residual stress in apolarizing plate etc. to prevent discoloration and coloring failure.

BEST MODE FOR CARRYING OUT THE INVENTION

The high-molecular weight acrylic polymer (A) of the present inventioncontains at least 50 wt % alkyl (meth)acrylate having an alkyl groupwith 5 or more carbon atoms and 0.2 to 2 wt % unsaturated carboxylicacid as the monomer unit. In the present invention, the alkyl(meth)acrylate refers to alkyl acrylate and/or alkyl methacrylate. Theterm “(meth)” is used in this meaning in this specification.

The alkyl group in the alkyl (meth)acrylate is not particularly limitedinsofar as it is an alkyl group containing 5 or more carbon atoms, butthe number of carbon atoms in the alkyl group is preferably 16 or less,more preferably 5 to 16, still more preferably 6 to 10, from theviewpoint of lower glass transition point and modulus of elasticity. Thealkyl group containing 5 or more carbon atoms may be a linear orbranched chain, but is preferably a branched chain for lower glasstransition point.

The alkyl (meth)acrylate containing 5 or more carbon atoms includes, forexample, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl(meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate etc.These may be used singly or as a mixture of two or more thereof.

The acrylic polymer (A) contains at least 50 wt % alkyl (meth)acrylatehaving an alkyl group containing 5 or more carbon atoms as the monomerunit. The content of the alkyl (meth)acrylate is preferably 60 to 90 wt%. It is not preferable that the content of the alkyl (meth)acrylate isless than 50% by weight, because stress relaxation is insufficient.

The unsaturated carboxylic acid includes acrylic acid, methacrylic acid,itaconic acid, maleic acid etc. An anhydride thereof can also be used.Among these compounds, acrylic acid and methacrylic acid are preferablyused.

The acrylic polymer (A) contains 0.2 to 2 wt %, preferably 0.3 to 1.5 wt% unsaturated carboxylic acid as the monomer unit. A content outside ofthis range is not preferable because when the content of the unsaturatedcarboxylic acid is higher than 2 wt %, the adhesion of the resultingcomposition to a liquid crystal cell is too high, while when the contentis less than 0.2 wt %, durability is adversely affected.

The acrylic polymer (A) may contain other monomers insofar as the alkyl(meth)acrylate having an alkyl group with 5 or more carbon atoms and theunsaturated carboxylic acid are contained in the above ratios as themonomer unit. The other monomers include an alkyl (meth)acrylate havinga C₁ to C₄ alkyl group, such as methyl (meth)acrylate, ethyl(meth)acrylate and butyl (meth)acrylate, a hydroxyl group-containingmonomer such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylateand N-methylol (meth)acrylamide; an epoxy group-containing monomer suchas glycidyl (meth)acrylate; and a nitrogen-containing monomer such as(meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, (meth)acryloylmorpholine,(meth)acetonitrile, vinylpyrrolidone, N-cyclohexylmaleimide, itaconimideand N,N-dimethylaminoethyl(meth)acrylamide. Further, vinyl acetate,styrene etc. can also be used. These monomers can be used singly or as amixture of two or more thereof.

The other monomers are preferably those having a functional groupreactive with a crosslinking agent. Particularly, a hydroxylgroup-containing monomer is preferable. The content of the monomerhaving a functional group reactive with a crosslinking agent ispreferably 0.02 to 1 wt %. The content is more preferably 0.04 to 0.4 wt%.

The weight-average molecular weight (determined by GPC; any molecularweights shown below were also determined by GPC) of the acrylic polymer(A) is 500,000 or more. The weight-average molecular weight ispreferably 600,000 or more. When the weight-average molecular weight isless than 500,000, durability is insufficient. On the other hand, theweight-average molecular weight of the acrylic polymer (A) is preferably1,500,000 or less, more preferably 1,200,000 or less, from the viewpointof operativeness.

In production of the acrylic polymer (A), a known radical polymerizationmethod such as solution polymerization, bulk polymerization and emulsionpolymerization can be suitably selected. As the radical polymerizationinitiator, a wide variety of known azo- or peroxide-based polymerizationinitiators can be used. For example, a solution polymerization initiatorsuch as azobisisobutyronitrile is used in an amount of about 0.01 to 0.2part by weight relative to 100 parts by weight of the total monomers. Asthe polymerization solvent, a solvent such as ethyl acetate or tolueneis used. The reaction is carried out usually at about 50 to 70° C. forabout 8 to 15 hours in an inert gas stream such as nitrogen.

The acrylic polymer (B) comprises at least 70 wt % alkyl (meth)acrylateand 1 to 7 wt % unsaturated carboxylic acid as the monomer unit andhaving a higher carboxylic acid equivalent than that of the acrylicpolymer (A).

The number of carbon atoms in the alkyl group in the alkyl(meth)acrylate is not particularly limited, but is preferably 1 to 4,from the viewpoint of hydrophilicity and flexibility. The alkyl(meth)acrylate having a C₁ to C₄ alkyl group includes, for example,methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate etc.The alkyl (meth)acrylate having a C₁ to C₄ alkyl group is used in anamount of preferably 50 wt % or more, more preferably 60 wt % or more.These may be used singly or as a mixture of two or more thereof.

The acrylic polymer (B) contains at least 70 wt % of the alkyl(meth)acrylate as the monomer unit. The content of the alkyl(meth)acrylate is preferably 80 to 96 wt %. It is not preferable thatthe content of the alkyl (meth)acrylate is less than 70 wt %, becausehydrophilicity is insufficient.

The unsaturated carboxylic acid can be exemplified by those illustratedin the acrylic polymer (A). The acrylic polymer (B) contains theunsaturated carboxylic acid in an amount of 1 to 7 wt %, preferably 2 to6 wt %, as the monomer unit. It is not preferable that the content ofthe unsaturated carboxylic acid is higher than 7 wt %, because stressrelaxation is lowered. A content of less than 1 wt % is not preferableeither because adhesion to a liquid crystal cell is increased.

The content of the unsaturated carboxylic acid is regulated such thatthe carboxylic acid equivalent of the acrylic polymer (B) is higher thanthe carboxylic acid equivalent of the acrylic polymer (A). It is notpreferable for the carboxylic acid equivalent of the acrylic polymer (B)to be lower than the carboxylic acid equivalent of the acrylic polymer(A), because adhesion to a liquid crystal cell is increased. Thecarboxylic acid equivalent is the amount of carboxylic acid group per 1g of the polymer, and for example, in the case of carboxylic acidderived from acrylic acid, the carboxylic acid equivalent (equivalent/g)is calculated by dividing, with the molecular weight of acrylic acid,the weight of acrylic acid in 1 g of the polymer.

The acrylic polymer (B) can contain other monomers insofar as itcontains the alkyl (meth)acrylate and the unsaturated carboxylic acid asthe monomer unit in the above ratios. The other monomers can beexemplified by those illustrated in the acrylic polymer (A).

The weight-average molecular weight of the acrylic polymer (B) is 2,000to 50,000, preferably 5,000 to 40,000. When the weight-average molecularweight is less than 2,000, durability is deteriorated. On the otherhand, it is not preferable for the weight-average molecular weight ofthe acrylic polymer (B) to be higher than 50,000, because adhesion to aliquid crystal cell is increased.

The acrylic polymer (B) can be produced in the same manner as inproduction of the acrylic polymer (A). The weight-average molecularweight can be regulated by using a large amount of a polymerizationinitiator or by using a chain transfer agent such as mercaptan.

As the silane coupling agent, a conventionally known one can be usedwithout particular limitation. Examples include an epoxygroup-containing silane coupling agents such as3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilaneand 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; an aminogroup-containing silane coupling agents such as3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane and3-triethoxysilyl-N-(1,3-dimethylbutylidene) propylamine; a (meth)acrylgroup-containing silane coupling agents such as3-acryloxypropyltrimethoxysilane and3-methacryloxypropyltriethoxysilane; and an isocyanate group-containingsilane coupling agents such as 3-isocyanatopropyltriethoxysilane.

The crosslinking agent is a multifunctional compound, which can reactwith carboxylic acid groups in the acrylic polymer (A), further withother functional groups, to form a crosslinked structure. When hydroxylgroups are introduced as functional groups, the crosslinking agent formsa crosslinked structure with the hydroxyl groups. The crosslinking agentincludes, for example, tolylene diisocyanate, diphenyl methanediisocyanate, polyisocyanate compounds such as various polyols havingdiisocyanate compounds added thereto, epoxy compounds, aziridinecompounds, melamine compounds, metal salts, and metal chelate compounds.Among these compounds, the polyisocyanate compounds are preferably used.Particularly, it is preferable that when the acrylic polymer (A) isproduced, hydroxy-containing monomers such as 2-hydroxyethyl acrylateare copolymerized, and when hydroxyl groups are introduced into theacrylic polymer (A), a crosslinked structure of the acrylic polymer (A)is formed by using a polyisocyanate compound as a crosslinked agent.

The pressure sensitive adhesive composition for optical membersaccording to the present invention comprises the high-molecular weightacrylic polymer (A), the low-molecular weight acrylic polymer (B), asilane coupling agent and a crosslinking agent. The amount of theacrylic polymer (B) to be blended is 0.1 to 4 parts by weight,preferably 0.1 to 2 parts by weight, relative to 100 parts by weight ofthe acrylic polymer (A). An amount outside of this range is notpreferable because when the acrylic polymer (B) is blended in an amountof higher than 4 parts by weight, durability is adversely affected,while when the amount is less than 0.1 part by weight, the adhesion to aliquid crystal cell is increased. In consideration of peeling propertiesafter storage for a long time, the amount of the acrylic polymer (B) tobe blended is particularly preferably 0.2 to 1 part by weight relativeto 100 parts by weight of the acrylic polymer (A). When the amount ofthe acrylic polymer (B) to be blended is higher than 1 part by weight,the adhesion tends to be slightly increased after storage for a longtime. When the amount is less than 0.2 part by weight, it tends to bedifficult to prevent the adhesion from increasing after storage for along time.

The silane coupling agent is incorporated in an amount of 0.01 to 1 partby weight, preferably 0.02 to 0.6 part by weight, relative to 100 partsby weight of the acrylic polymer (A). A content outside this range isnot preferable because when the content of the silane coupling agent ishigher than 1 part by weight, the adhesion of the resulting compositionto a liquid crystal cell is increased, while when the content is lessthan 0.01 part by weight, durability is deteriorated.

The amount of the crosslinking agent to be incorporated is notparticularly limited, but preferably the crosslinking agent isincorporated such that the gel fraction of the resulting crosslinkedpressure sensitive adhesive layer is 35 to 90 wt %. The amount thecrosslinking agent to be incorporated is regulated more preferably suchthat the gel fraction is 40 to 80 wt %. When the gel fraction is low,durability tends to be insufficient, while when the gel fraction ishigh, stress relaxation tends to be insufficient. For regulation of gelfraction, the amount of the crosslinking agent to be incorporated into100 parts by weight of the acrylic polymer (A) is usually 0.01 to 5parts by weight, more preferably 0.02 to 2 parts by weight, depending onthe material to be used.

The gel fraction of the pressure sensitive adhesive layer is calculatedfrom the following equation:

Gel fraction (wt %)=(W2/W1)×100

wherein W1 is the dry weight (g) of a pressure sensitive adhesive layer,and W2 is the weight (g) of the pressure sensitive adhesive layer whichwas dipped in ethyl acetate at room temperature (23° C.) for 7 days,then removed and dried.

Specifically, the gel fraction is determined in the following manner.That is, a solution of the pressure sensitive adhesive composition isapplied onto a film subjected to release treatment, then dried at 110°C. for 5 minutes and aged at 50° C. for 24 hours, and a predeterminedamount (about 500 mg) W1 (g) of the resulting adhesive is collected.Then, this adhesive is left in ethyl acetate for 7 days at roomtemperature, and then the gel is removed and dried at 130° C. for 2hours to measure the weight W2 (g) of the gel. The gel fraction isdetermined by using the determined weight (W1 and W2) in the aboveformula.

The pressure sensitive adhesive composition for optical membersaccording to the present invention can blended if necessary with an UVabsorber, aging inhibitor, softener, dye, pigment, filler etc.

The pressure sensitive adhesive optical member of the present inventionis obtained by forming a pressure sensitive adhesive layer of thepressure sensitive adhesive composition for optical members, on one sideor both sides of an optical member.

The method of forming the pressure sensitive adhesive layer on anoptical member includes, but is not limited to, a method wherein thepressure sensitive adhesive composition is applied onto a release liner,then dried and crosslinked to form a pressure sensitive adhesive layerwhich is then transferred onto an optical member, and a method whereinthe pressure sensitive adhesive composition is applied directly onto anoptical member, dried and crosslinked to form a pressure sensitiveadhesive layer. For application, any arbitrary coating methods using aroll coater such as a reverse coater or a gravure coater, a curtaincoater, a lip coater or a die coater can be used. The thickness of thepressure sensitive adhesive layer after drying is usually 2 to 500 μm,preferably 5 to 100 μm.

When the pressure sensitive adhesive layer is exposed to the surface ofa support material or the like, the pressure sensitive adhesive layer isprotected until use with a sheet subjected to release treatment. Thematerial constituting the release sheet includes paper, a film ofsynthetic resin such as polyethylene, polypropylene or polyethyleneterephthalate, rubber sheet, paper, cloth, nonwoven fabric, net, foamedsheet and metal foil, as well as a suitable film such as a laminatethereof. The surface of the release sheet may be subjected to releasetreatment such as silicone treatment, long-chain alkyl treatment orfluorine treatment in order to improve releasability from the pressuresensitive adhesive layer, if necessary.

As optical members, members used for formation of image displays, suchas liquid crystal displays, may be used, and kinds are not especiallylimited. For example, polarizing plates may be mentioned as opticalmembers. As polarizing plates, in general a polarizing plate havingtransparent protective film one side or both sides of a polarizer isused.

A polarizer is not limited especially but various kinds of polarizer maybe used. As a polarizer, for example, a film that is uniaxiallystretched after having dichromatic substances, such as iodine anddichromatic dye, absorbed to hydrophilic high molecular weight polymerfilms, such as polyvinyl alcohol type film, partially formalizedpolyvinyl alcohol type film, and ethylene-vinyl acetate copolymer typepartially saponified film; poly-ene type orientation films, such asdehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride,etc. may be mentioned. In these, a polyvinyl alcohol type film on whichdichromatic materials (iodine, dyes) is absorbed and oriented afterstretched is suitably used. Although thickness of polarizer is notespecially limited, the thickness of about 5 to 80 μm is commonlyadopted.

A polarizer that is uniaxially stretched after a polyvinyl alcohol typefilm dyed with iodine is obtained by stretching a polyvinyl alcohol filmby 3 to 7 times the original length, after dipped and dyed in aqueoussolution of iodine. If needed the film may also be dipped in aqueoussolutions, such as boric acid and potassium iodide, which may includezinc sulfate, zinc chloride. Furthermore, before dyeing, the polyvinylalcohol type film may be dipped in water and rinsed if needed. Byrinsing polyvinyl alcohol type film with water, effect of preventingun-uniformity, such as unevenness of dyeing, is expected by makingpolyvinyl alcohol type film swelled in addition that also soils andblocking inhibitors on the polyvinyl alcohol type film surface may bewashed off. Stretching may be applied after dyed with iodine or may beapplied concurrently, or conversely dyeing with iodine may be appliedafter stretching. Stretching is applicable in aqueous solutions, such asboric acid and potassium iodide, and in water bath.

As the protective film prepared on one side or both sides of thepolarizer, materials is excellent in transparency, mechanical strength,heat stability, water shielding property, isotropy, etc. may bepreferably used. As materials of the above-mentioned protective layer,for example, polyester type polymers, such as polyethylene terephthalateand polyethylenenaphthalate; cellulose type polymers, such as diacetylcellulose and triacetyl cellulose; acrylics type polymer, such as polymethylmethacrylate; styrene type polymers, such as polystyrene andacrylonitrile-styrene copolymer (AS resin); polycarbonate type polymermay be mentioned. Besides, as examples of the polymer forming aprotective film, polyolefin type polymers, such as polyethylene,polypropylene, polyolefin that has cyclo-type or norbornene structure,ethylene-propylene copolymer; vinyl chloride type polymer; amide typepolymers, such as nylon and aromatic polyamide; imide type polymers;sulfone type polymers; polyether sulfone type polymers; polyether-etherketone type polymers; poly phenylene sulfide type polymers; vinylalcohol type polymer; vinylidene chloride type polymers; vinyl butyraltype polymers; allylate type polymers; polyoxymethylene type polymers;epoxy type polymers; or blend polymers of the above-mentioned polymersmay be mentioned. Films made of heat curing type or ultraviolet raycuring type resins, such as acryl based, urethane based, acryl urethanebased, epoxy based, and silicone based, etc. may be mentioned.

Moreover, as is described in Japanese Patent Laid-Open Publication No.2001-343529 (WO 01/37007), polymer films, for example, resincompositions including (A) thermoplastic resins having substitutedand/or non-substituted imido group is in side chain, and (B)thermoplastic resins having substituted and/or non-substituted phenyland nitrile group in side chain may be mentioned. As an illustrativeexample, a film may be mentioned that is made of a resin compositionincluding alternating copolymer comprising iso-butylene and N-methylmaleimide, and acrylonitrile-styrene copolymer. A film comprisingmixture extruded article of resin compositions etc. may be used.

In general, a thickness of the protection film, which can be determinedarbitrarily, is 500 μm or less, preferably 1 through 300 μm, andespecially preferably 5 through 300 g/m in viewpoint of strength, workhandling and thin layer

Moreover, it is preferable that the protective film may have as littlecoloring as possible. Accordingly, a protective film having a phasedifference value in a film thickness direction represented byRth=[(nx+ny)/2−nz]×d of −90 nm through +75 nm (where, nx and nyrepresent principal indices of refraction in a film plane, nz representsrefractive index in a film thickness direction, and d represents a filmthickness) may be preferably used. Thus, coloring (optical coloring) ofpolarizing plate resulting from a protective film may mostly becancelled using a protective film having a phase difference value (Rth)of −90 nm through +75 nm in a thickness direction. The phase differencevalue (Rth) in a thickness direction is preferably −80 nm through +60nm, and especially preferably −70 nm through +45 nm.

As a protective film, if polarization property and durability are takeninto consideration, cellulose based polymer, such as triacetylcellulose, is preferable, and especially triacetyl cellulose film issuitable. In addition, when the protective films are provided on bothsides of the polarizer, the protective films comprising same polymermaterial may be used on both of a front side and a back side, and theprotective films comprising different polymer materials etc. may beused. Adhesives are used for adhesion processing of the above describedpolarizer and the protective film. As adhesives, isocyanate derivedadhesives, polyvinyl alcohol derived adhesives, gelatin derivedadhesives, vinyl polymers derived latex type, aqueous polyurethane basedadhesives, aqueous polyesters derived adhesives, etc. may be mentioned.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed protective film has not been adhered.

A hard coat processing is applied for the purpose of protecting thesurface of the polarizing plate from damage, and this hard coat film maybe formed by a method in which, for example, a curable coated film withexcellent hardness, slide property etc. is added on the surface of theprotective film using suitable ultraviolet curable type resins, such asacrylic type and silicone type resins. Antireflection processing isapplied for the purpose of antireflection of outdoor daylight on thesurface of a polarizing plate and it may be prepared by forming anantireflection film according to the conventional method etc. Besides, asticking prevention processing is applied for the purpose of adherenceprevention with adjoining layer.

In addition, an anti glare processing is applied in order to prevent adisadvantage that outdoor daylight reflects on the surface of apolarizing plate to disturb visual recognition of transmitting lightthrough the polarizing plate, and the processing may be applied, forexample, by giving a fine concavo-convex structure to a surface of theprotective film using, for example, a suitable method, such as roughsurfacing treatment method by sandblasting or embossing and a method ofcombining transparent fine particle. As a fine particle combined inorder to form a fine concavo-convex structure on the above-mentionedsurface, transparent fine particles whose average particle size is 0.5to 50 μm, for example, such as inorganic type fine particles that mayhave conductivity comprising silica, alumina, titania, zirconia, tinoxides, indium oxides, cadmium oxides, antimony oxides, etc., andorganic type fine particles comprising cross-linked of non-cross-linkedpolymers may be used. When forming fine concavo-convex structure on thesurface, the amount of fine particle used is usually about 2 to 50weight part to the transparent resin 100 weight part that forms the fineconcavo-convex structure on the surface, and preferably 5 to 25 weightpart. An anti glare layer may serve as a diffusion layer (viewing angleexpanding function etc.) for diffusing transmitting light through thepolarizing plate and expanding a viewing angle etc.

In addition, the above-mentioned antireflection layer, stickingprevention layer, diffusion layer, anti glare layer, etc. may be builtin the protective film itself and also they may be prepared as anoptical layer different from the protective layer.

An optical member of the present invention is especially no limitationabout the optical layers, which may be used for formation of a liquidcrystal display etc., such as a reflector, a transflective plate, aretardation plate (a half wavelength plate and a quarter wavelengthplate included), and a viewing angle compensation film, may be used.

Especially preferable polarizing plates are; a reflection typepolarizing plate or a transflective type polarizing plate in which areflector or a transflective reflector is further laminated onto apolarizing plate of the present invention; an elliptically polarizingplate or a circular polarizing plate in which a retardation plate isfurther laminated onto the polarizing plate; a wide viewing anglepolarizing plate in which a viewing angle compensation film is furtherlaminated onto the polarizing plate; or a polarizing plate in which abrightness enhancement film is further laminated onto the polarizingplate.

A reflective layer is prepared on a polarizing plate to give areflection type polarizing plate, and this type of plate is used for aliquid crystal display in which an incident light from a view side(display side) is reflected to give a display. This type of plate doesnot require built-in light sources, such as a backlight, but has anadvantage that a liquid crystal display may easily be made thinner. Areflection type polarizing plate may be formed using suitable methods,such as a method in which a reflective layer of metal etc. is, ifrequired, attached to one side of a polarizing plate through atransparent protective layer etc.

As an example of a reflection type polarizing plate, a plate may bementioned on which, if required, a reflective layer is formed using amethod of attaching a foil and vapor deposition film of reflectivemetals, such as aluminum, to one side of a matte treated protectivefilm. Moreover, a different type of plate with a fine concavo-convexstructure on the surface obtained by mixing fine particle into theabove-mentioned protective film, on which a reflective layer ofconcavo-convex structure is prepared, may be mentioned. The reflectivelayer that has the above-mentioned fine concavo-convex structurediffuses incident light by random reflection to prevent directivity andglaring appearance, and has an advantage of controlling unevenness oflight and darkness etc. Moreover, the protective film containing thefine particle has an advantage that unevenness of light and darkness maybe controlled more effectively, as a result that an incident light andits reflected light that is transmitted through the film are diffused. Areflective layer with fine concavo-convex structure on the surfaceeffected by a surface fine concavo-convex structure of a protective filmmay be formed by a method of attaching a metal to the surface of atransparent protective layer directly using, for example, suitablemethods of a vacuum evaporation method, such as a vacuum depositionmethod, an ion plating method, and a sputtering method, and a platingmethod etc.

Instead of a method in which a reflection plate is directly given to theprotective film of the above-mentioned polarizing plate, a reflectionplate may also be used as a reflective sheet constituted by preparing areflective layer on the suitable film for the transparent film. Inaddition, since a reflective layer is usually made of metal, it isdesirable that the reflective side is covered with a protective film ora polarizing plate etc. when used, from a viewpoint of preventingdeterioration in reflectance by oxidation, of maintaining an initialreflectance for a long period of time and of avoiding preparation of aprotective layer separately etc.

In addition, a transflective type polarizing plate may be obtained bypreparing the above-mentioned reflective layer as a transflective typereflective layer, such as a half-mirror etc. that reflects and transmitslight. A transflective type polarizing plate is usually prepared in thebackside of a liquid crystal cell and it may form a liquid crystaldisplay unit of a type in which a picture is displayed by an incidentlight reflected from a view side (display side) when used in acomparatively well-lighted atmosphere. And this unit displays a picture,in a comparatively dark atmosphere, using embedded type light sources,such as a back light built in backside of a transflective typepolarizing plate. That is, the transflective type polarizing plate isuseful to obtain of a liquid crystal display of the type that savesenergy of light sources, such as a back light, in a well-lightedatmosphere, and can be used with a built-in light source if needed in acomparatively dark atmosphere etc.

The above-mentioned polarizing plate may be used as ellipticallypolarizing plate or circularly polarizing plate on which the retardationplate is laminated. A description of the above-mentioned ellipticallypolarizing plate or circularly polarizing plate will be made in thefollowing paragraph. These polarizing plates change linearly polarizedlight into elliptically polarized light or circularly polarized light,elliptically polarized light or circularly polarized light into linearlypolarized light or change the polarization direction of linearlypolarization by a function of the retardation plate. As a retardationplate that changes circularly polarized light into linearly polarizedlight or linearly polarized light into circularly polarized light, whatis called a quarter wavelength plate (also called ¼ plate) is used.Usually, half-wavelength plate (also called ½ plate) is used, whenchanging the polarization direction of linearly polarized light.

Elliptically polarizing plate is effectively used to give a monochromedisplay without above-mentioned coloring by compensating (preventing)coloring (blue or yellow color) produced by birefringence of a liquidcrystal layer of a super twisted nematic (STN) type liquid crystaldisplay. Furthermore, a polarizing plate in which three-dimensionalrefractive index is controlled may also preferably compensate (prevent)coloring produced when a screen of a liquid crystal display is viewedfrom an oblique direction. Circularly polarizing plate is effectivelyused, for example, when adjusting a color tone of a picture of areflection type liquid crystal display that provides a colored picture,and it also has function of antireflection.

As retardation plates, birefringent films obtained by uniaxially orbiaxially stretched polymer materials, oriented films of liquid crystalpolymers, oriented layers of liquid crystal polymers currently supportedwith films may be mentioned. A thickness of the retardation plate isalso not especially limited, and it is about 20 to 150 μm in general.

As polymer material, for example, there may be mentioned: polyvinylalcohols, polyvinyl butyrals, polymethyl vinyl ethers, polyhydroxy ethylacrylates, hydroxyethyl celluloses, hydroxy propyl celluloses, methylcelluloses, polycarbonates, polyallylates, polysulfones, polyethyleneterephthalates, polyethylene naphthalates, polyethersulfones,polyphenylene sulfides, polyphenylene oxides, polyallyl sulfones,polyamides, polyimides, polyolefins, polyvinyl chlorides, cellulose typepolymers, and norbornene based resins, or binary or ternary copolymers,graft copolymers, and blend object thereof. These polymer materials arestretched to obtain an oriented object that is stretched film.

As liquid crystalline polymers, for example, various kinds of polymersof principal chain type and side chain type in which conjugated linearatomic groups (mesogens) conferring liquid crystalline orientation areintroduced into a principal chain and a side chain of a polymer may bementioned. As examples of principal chain type liquid crystallinepolymers, polymers having a structure where mesogen groups are bonded byspacer parts conferring flexibility, for example, polyester based liquidcrystalline polymers having nematic orientation property, discoticpolymers, cholesteric polymers, etc. may be mentioned. As examples ofside chain type liquid crystalline polymers, polymers havingpolysiloxanes, polyacrylates, polymethacrylates, or polymalonates as aprincipal chain skeleton, and having mesogen parts comprisingpara-substituted cyclic compound units conferring nematic orientationproperty as side chains via spacer parts comprising conjugated atomicgroups may be mentioned. These liquid crystal polymer, for example, isaligned by developing a solution of a liquid crystal polymer on anorientation treated surface where rubbing treatment was performed to asurface of thin films, such as polyimide and polyvinyl alcohol, formedon a glass plate, or where silicon oxide is deposited by an obliqueevaporation method, and then by heat-treating. Retardation plates thathave suitable phase difference depending on the purpose of use, such asaiming at compensation of coloring or viewing angle using birefringence,for example, various wavelength plates and liquid crystal layers, may beused. In addition retardation plates in which two or more kinds ofretardation plates are laminated together to control optical properties,such as phase difference may be used.

The above-mentioned elliptically polarizing plate and an above-mentionedreflected type elliptically polarizing plate are laminated platecombining suitably a polarizing plate or a reflection type polarizingplate with a retardation plate. This type of elliptically polarizingplate etc. may be manufactured by combining a polarizing plate(reflected type) and a retardation plate, and by laminating them one byone separately in the manufacture process of a liquid crystal display.On the other hand, the polarizing plate in which lamination wasbeforehand carried out and was obtained as an optical member, such as anelliptically polarizing plate, is excellent in a stable quality, aworkability in lamination etc., and has an advantage in improvedmanufacturing efficiency of a liquid crystal display.

A viewing angle compensation film is a film for extending viewing angleso that a picture may look comparatively clearly, even when it is viewedfrom an oblique direction not from vertical direction to a screen. Assuch a viewing angle compensation retardation plate, in addition, a filmhaving birefringence property that is processed by uniaxial stretchingor orthogonal biaxial stretching and a bi-directional stretched film asinclined orientation film etc. may be used. As inclined orientationfilm, for example, a film obtained using a method in which a heatshrinking film is adhered to a polymer film, and then the combined filmis heated and stretched or shrinked under a condition of beinginfluenced by a shrinking force, or a film that is oriented in obliquedirection may be mentioned. The viewing angle compensation film issuitably combined for the purpose of prevention of coloring caused bychange of visible angle based on retardation by liquid crystal cell etc.and of expansion of viewing angle with good visibility.

Besides, a compensation plate in which an optical anisotropy layerconsisting of an alignment layer of liquid crystal polymer, especiallyconsisting of an inclined alignment layer of discotic liquid crystalpolymer is supported with triacetyl cellulose film may preferably beused from a viewpoint of attaining a wide viewing angle with goodvisibility.

The polarizing plate with which a polarizing plate and a brightnessenhancement film are adhered together is usually used being prepared ina backside of a liquid crystal cell. A brightness enhancement film showsa characteristic that reflects linearly polarized light with apredetermined polarization axis, or circularly polarized light with apredetermined direction, and that transmits other light, when naturallight by back lights of a liquid crystal display or by reflection from aback-side etc., comes in. The polarizing plate, which is obtained bylaminating a brightness enhancement film to a polarizing plate, thusdoes not transmit light without the predetermined polarization state andreflects it, while obtaining transmitted light with the predeterminedpolarization state by accepting a light from light sources, such as abacklight. This polarizing plate makes the light reflected by thebrightness enhancement film further reversed through the reflectivelayer prepared in the backside and forces the light re-enter into thebrightness enhancement film, and increases the quantity of thetransmitted light through the brightness enhancement film bytransmitting a part or all of the light as light with the predeterminedpolarization state. The polarizing plate simultaneously suppliespolarized light that is difficult to be absorbed in a polarizer, andincreases the quantity of the light usable for a liquid crystal picturedisplay etc., and as a result luminosity may be improved. That is, inthe case where the light enters through a polarizer from backside of aliquid crystal cell by the back light etc. without using a brightnessenhancement film, most of the light, with a polarization directiondifferent from the polarization axis of a polarizer, is absorbed by thepolarizer, and does not transmit through the polarizer. This means thatalthough influenced with the characteristics of the polarizer used,about 50 percent of light is absorbed by the polarizer, the quantity ofthe light usable for a liquid crystal picture display etc. decreases somuch, and a resulting picture displayed becomes dark. A brightnessenhancement film does not enter the light with the polarizing directionabsorbed by the polarizer into the polarizer but reflects the light onceby the brightness enhancement film, and further makes the light reversedthrough the reflective layer etc. prepared in the backside to re-enterthe light into the brightness enhancement film. By this above-mentionedrepeated operation, only when the polarization direction of the lightreflected and reversed between the both becomes to have the polarizationdirection which may pass a polarizer, the brightness enhancement filmtransmits the light to supply it to the polarizer. As a result, thelight from a backlight may be efficiently used for the display of thepicture of a liquid crystal display to obtain a bright screen.

A diffusion plate may also be prepared between brightness enhancementfilm and the above described reflective layer, etc. A polarized lightreflected by the brightness enhancement film goes to the above describedreflective layer etc., and the diffusion plate installed diffusespassing light uniformly and changes the light state into depolarizationat the same time. That is, the diffusion plate returns polarized lightto natural light state. Steps are repeated where light, in theunpolarized state, i.e., natural light state, reflects throughreflective layer and the like, and again goes into brightnessenhancement film through diffusion plate toward reflective layer and thelike. Diffusion plate that returns polarized light to the natural lightstate is installed between brightness enhancement film and the abovedescribed reflective layer, and the like, in this way, and thus auniform and bright screen may be provided while maintaining brightnessof display screen, and simultaneously controlling non-uniformity ofbrightness of the display screen. By preparing such diffusion plate, itis considered that number of repetition times of reflection of a firstincident light increases with sufficient degree to provide uniform andbright display screen conjointly with diffusion function of thediffusion plate.

The suitable films are used as the above-mentioned brightnessenhancement film. Namely, multilayer thin film of a dielectricsubstance; a laminated film that has the characteristics of transmittinga linearly polarized light with a predetermined polarizing axis, and ofreflecting other light, such as the multilayer laminated film of thethin film having a different refractive-index anisotropy (D-BEF andothers manufactured by 3M Co., Ltd.); an aligned film of cholestericliquid-crystal polymer; a film that has the characteristics ofreflecting a circularly polarized light with either left-handed orright-handed rotation and transmitting other light, such as a film onwhich the aligned cholesteric liquid crystal layer is supported (PCF350manufactured by NITTO DENKO CORPORATION, Transmax manufactured by MerckCo., Ltd., and others); etc. may be mentioned.

Therefore, in the brightness enhancement film of a type that transmits alinearly polarized light having the above-mentioned predeterminedpolarization axis, by arranging the polarization axis of the transmittedlight and entering the light into a polarizing plate as it is, theabsorption loss by the polarizing plate is controlled and the polarizedlight can be transmitted efficiently. On the other hand, in thebrightness enhancement film of a type that transmits a circularlypolarized light as a cholesteric liquid-crystal layer, the light may beentered into a polarizer as it is, but it is desirable to enter thelight into a polarizer after changing the circularly polarized light toa linearly polarized light through a retardation plate, taking controlan absorption loss into consideration. In addition, a circularlypolarized light is convertible into a linearly polarized light using aquarter wavelength plate as the retardation plate.

A retardation plate that works as a quarter wavelength plate in a widewavelength ranges, such as a visible-light band, is obtained by a methodin which a retardation layer working as a quarter wavelength plate to apale color light with a wavelength of 550 nm is laminated with aretardation layer having other retardation characteristics, such as aretardation layer working as a half-wavelength plate. Therefore, theretardation plate located between a polarizing plate and a brightnessenhancement film may consist of one or more retardation layers.

In addition, also in a cholesteric liquid-crystal layer, a layerreflecting a circularly polarized light in a wide wavelength ranges,such as a visible-light band, may be obtained by adopting aconfiguration structure in which two or more layers with differentreflective wavelength are laminated together. Thus a transmittedcircularly polarized light in a wide wavelength range may be obtainedusing this type of cholesteric liquid-crystal layer.

Moreover, the polarizing plate may consist of multi-layered film oflaminated layers of a polarizing plate and two of more of optical layersas the above-mentioned separated type polarizing plate. Therefore, apolarizing plate may be a reflection type elliptically polarizing plateor a semi-transmission type elliptically polarizing plate, etc. in whichthe above-mentioned reflection type polarizing plate or a transflectivetype polarizing plate is combined with above described retardation platerespectively. Although an optical member with the above describedoptical layer laminated to the polarizing plate may be formed by amethod in which laminating is separately carried out sequentially inmanufacturing process of a liquid crystal display etc., an opticalmember in a form of being laminated beforehand has an outstandingadvantage that it has excellent stability in quality and assemblyworkability, etc., and thus manufacturing processes ability of a liquidcrystal display etc. may be raised. Proper adhesion means, such as apressure sensitive adhesive layer, may be used for laminating. On theoccasion of adhesion of the above described polarizing plate and otheroptical members, the optical axis may be set as a suitable configurationangle according to the target retardation characteristics etc.

In addition, in the present invention, ultraviolet absorbing propertymay be given to the above-mentioned each layer, such as a pressuresensitive adhesive optical member, an optical member etc. and anpressure sensitive adhesive layer, using a method of adding UVabsorbents, such as salicylic acid ester type compounds, benzophenoltype compounds, benzotriazol type compounds, cyano acrylate typecompounds, and nickel complex salt type compounds.

A pressure sensitive adhesive optical member of the present inventionmay be preferably used for manufacturing various equipment, such asliquid crystal display, etc. Assembling of a liquid crystal display maybe carried out according to conventional methods. That is, a liquidcrystal display is generally manufactured by suitably assembling severalparts such as a liquid crystal cell, optical members and, if necessity,lighting system, and by incorporating driving circuit. In the presentinvention, except that an optical member by the present invention isused, there is especially no limitation to use any conventional methods.Also any liquid crystal cell of arbitrary type, such as TN type, and STNtype, π type may be used. And above-mentioned IPS type, VA type may beused.

Suitable liquid crystal displays, such as liquid crystal display withwhich the above-mentioned pressure sensitive adhesive optical member hasbeen located at one side or both sides of the liquid crystal cell, andwith which a backlight or a reflector is used for a lighting system maybe manufactured. In this case, the pressure sensitive adhesive opticalmember by the present invention may be installed in one side or bothsides of the liquid crystal cell. When installing the optical members inboth sides, they may be of the same type or of different type.Furthermore, in assembling a liquid crystal display, suitable parts,such as diffusion plate, anti-glare layer, antireflection film,protective plate, prism array, lens array sheet, optical diffusionplate, and backlight, may be installed in suitable position in one layeror two or more layers.

Subsequently, organic electro luminescence equipment (organic ELdisplay) will be explained. Generally, in organic EL display, atransparent electrode, an organic emitting layer and a metal electrodeare laminated on a transparent substrate in an order configuring anilluminant (organic electro luminescence illuminant). Here, an organicemitting layer is a laminated material of various organic thin films,and much compositions with various combination are known, for example, alaminated material of hole injection layer comprising triphenylaminederivatives etc., an emitting layer comprising fluorescent organicsolids, such as anthracene; a laminated material of electronic injectionlayer comprising such an emitting layer and perylene derivatives, etc.;laminated material of these hole injection layers, emitting layer, andelectronic injection layer etc.

An organic EL display emits light based on a principle that positivehole and electron are injected into an organic emitting layer byimpressing voltage between a transparent electrode and a metalelectrode, the energy produced by recombination of these positive holesand electrons excites fluorescent substance, and subsequently light isemitted when excited fluorescent substance returns to ground state. Amechanism called recombination which takes place in a intermediateprocess is the same as a mechanism in common diodes, and, as isexpected, there is a strong non-linear relationship between electriccurrent and luminescence strength accompanied by rectification nature toapplied voltage.

In an organic EL display, in order to take out luminescence in anorganic emitting layer, at least one electrode must be transparent. Thetransparent electrode usually formed with transparent electricconductor, such as indium tin oxide (ITO), is used as an anode. On theother hand, in order to make electronic injection easier and to increaseluminescence efficiency, it is important that a substance with smallwork function is used for cathode, and metal electrodes, such as Mg—Agand Al—Li, are usually used.

In organic EL display of such a configuration, a very thin film about 10nm forms an organic emitting layer in thickness. For this reason, lightis transmitted nearly completely through organic emitting layer asthrough transparent electrode. Consequently, since the light thatenters, when light is not emitted, as incident light from a surface of atransparent substrate and is transmitted through a transparent electrodeand an organic emitting layer and then is reflected by a metalelectrode, appears in front surface side of the transparent substrateagain, a display side of the organic EL display looks like mirror ifviewed from outside.

In an organic EL display containing an organic electro luminescenceilluminant equipped with a transparent electrode on a surface side of anorganic emitting layer that emits light by impression of voltage, and atthe same time equipped with a metal electrode on a back side of organicemitting layer, a retardation plate may be installed between thesetransparent electrodes and a polarizing plate, while preparing thepolarizing plate on the surface side of the transparent electrode.

Since the retardation plate and the polarizing plate have functionpolarizing the light that has entered as incident light from outside andhas been reflected by the metal electrode, they have an effect of makingthe mirror surface of metal electrode not visible from outside by thepolarization action. If a retardation plate is configured with a quarterwavelength plate and the angle between the two polarization directionsof the polarizing plate and the retardation plate is adjusted to π/4,the mirror surface of the metal electrode may be completely covered.

This means that only linearly polarized light component of the externallight that enters as incident light into this organic EL display istransmitted with the work of polarizing plate. This linearly polarizedlight generally gives an elliptically polarized light by the retardationplate, and especially the retardation plate is a quarter wavelengthplate, and moreover when the angle between the two polarizationdirections of the polarizing plate and the retardation plate is adjustedto π/4, it gives a circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode and the organic thin film, and isreflected by the metal electrode, and then is transmitted through theorganic thin film, the transparent electrode and the transparentsubstrate again, and is turned into a linearly polarized light againwith the retardation plate. And since this linearly polarized light liesat right angles to the polarization direction of the polarizing plate,it cannot be transmitted through the polarizing plate. As the result,mirror surface of the metal electrode may be completely covered.

EXAMPLES

Hereinafter, the present invention is described in more detail byreference to the Examples, but the present invention is not limited bythe Examples. In the Examples, “parts” and “%” refer to “parts byweight” and “% by weight”, respectively.

Example 1 Preparation of High-Molecular Weight Acrylic Polymer (A)

70 parts of isononyl acrylate, 20 parts of butyl acrylate, 10 parts ofethyl acrylate, 1 part of acrylic acid, 0.1 part of 2-hydroxyethylacrylate, 0.1 part of 2,2′-azobisisobutyronitrile and 200 parts of ethylacetate were introduced into a four-necked flask equipped with anitrogen inlet tube and a condenser, then flushed sufficiently withnitrogen, and subjected to polymerization reaction at 55° C. for 12hours under stirring in a nitrogen stream to give a solution of acrylicpolymer (A1) having a weight-average molecular weight of 850,000. Thecarboxylic acid equivalent of the acrylic polymer (A1) was 1.37×10⁻⁴equivalent/g.

(Preparation of Low-Molecular Weight Acrylic Polymer (B))

80 parts of butyl acrylate, 15 parts of 2-ethylhexyl acrylate, 5 partsof acrylic acid, 0.8 part of lauryl mercaptan and 0.1 part of2,2′-azobisisobutyronitrile were introduced into a four-necked flaskequipped with a nitrogen inlet tube and a condenser, then flushedsufficiently with nitrogen, and subjected to polymerization reaction at55° C. for 12 hours under stirring in a nitrogen stream to give asolution of acrylic polymer (B1) having a weight-average molecularweight of 27,000. The carboxylic acid equivalent of the acrylic polymer(B1) was 6.89×10⁻⁴ equivalent/g.

(Preparation of a Pressure Sensitive Adhesive Composition for OpticalMembers)

0.5 part (solids content) of the acrylic polymer (B1) solution, 0.1 partof 3-glycidoxypropyltrimethoxysilane as a silane coupling agent, and 0.8part of a polyisocyanate-based crosslinking agent consisting of tolylenediisocyanate-added trimethylol propane as a crosslinking agent wereuniformly mixed with 100 parts (solids content) of the acrylic polymer(A1) solution to prepare a pressure sensitive adhesive composition foroptical members.

(Formation of a Pressure Sensitive Adhesive Optical Member)

The pressure sensitive adhesive composition was applied onto apolyethylene terephthalate film of 38 μm in thickness subjected tosilicone release treatment, such that the thickness of its pressuresensitive adhesive layer after drying was 25 μm, followed by drying andcrosslinking at 110° C. for 5 minutes to form a pressure sensitiveadhesive layer. The pressure sensitive adhesive layer was transferredonto a polarizing plate and subjected to aging treatment at 50° C. for24 hours, to give a pressure sensitive adhesive optical member. The gelfraction of the pressure sensitive adhesive layer was 45%.

Example 2

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount (solidscontent) of the acrylic polymer (B1) solution to be used was changed to0.2 part. Further, a pressure sensitive adhesive layer was formed in thesame manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 48%.

Example 3

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount (solidscontent) of the acrylic polymer (B1) solution to be used was changed to0.8 part. Further, a pressure sensitive adhesive layer was formed in thesame manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 43%.

Example 4

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that 0.02 part of anepoxy-based crosslinking agent(1,3-bis(N,N-diglycidylaminoethyl)cyclohexane) was used as thecrosslinking agent. Further, a pressure sensitive adhesive layer wasformed in the same manner as in Example 1 except that the above pressuresensitive adhesive composition was used, and also a pressure sensitiveadhesive optical member was obtained. The gel fraction of the pressuresensitive adhesive layer was 62%.

Example 5 Preparation of High-Molecular Weight Acrylic Polymer (A)

70 parts of 2-ethylhexyl acrylate, 30 parts of butyl acrylate, 0.5 partof acrylic acid, 0.1 part of 2-hydroxyethyl acrylate, 0.1 part of2,2′-azobisisobutyronitrile and 200 parts of ethyl acetate wereintroduced into a four-necked flask equipped with a nitrogen inlet tubeand a condenser, then flushed sufficiently with nitrogen, and subjectedto polymerization reaction at 55° C. for 12 hours under stirring in anitrogen stream to give a solution of acrylic polymer (A2) having aweight-average molecular weight of 950,000. The carboxylic acidequivalent of the acrylic polymer (A2) was 0.69×10⁻⁴ equivalent/g.

(Preparation of Low-Molecular Weight Acrylic Polymer (B))

100 parts of butyl acrylate, 5 parts of acrylic acid, 1 part of laurylmercaptan and 0.1 part of 2,2′-azobisisobutyronitrile were introducedinto a four-necked flask equipped with a nitrogen inlet tube and acondenser, then flushed sufficiently with nitrogen, and subjected topolymerization reaction at 55° C. for 12 hours under stirring in anitrogen stream to give a solution of acrylic polymer (B2) having aweight-average molecular weight of 21,000. The carboxylic acidequivalent of the acrylic polymer (B2) was 6.55×10⁻⁴ equivalent/g.

(Preparation of a Pressure Sensitive Adhesive Composition for OpticalMembers)

0.5 part (solids content) of the acrylic polymer (B2) solution, 0.1 partof 3-acryloxypropyltrimethoxysilane as a silane coupling agent, and 1part of a polyisocyanate-based crosslinking agent consisting of tolylenediisocyanate-added trimethylol propane as a crosslinking agent wereuniformly mixed with 100 parts (solids content) of the high-molecularweight polymer (A2) solution to prepare a pressure sensitive adhesivecomposition for optical members.

(Formation of a Pressure Sensitive Adhesive Optical Member)

The pressure sensitive adhesive composition was applied onto apolyethylene terephthalate film of 38 μm in thickness subjected tosilicone release treatment, such that the thickness of its pressuresensitive adhesive layer after drying was 25 μm, followed by drying andcrosslinking at 110° C. for 5 minutes to form a pressure sensitiveadhesive layer. The pressure sensitive adhesive layer was transferredonto a polarizing plate and subjected to aging treatment at 50° C. for24 hours, to give a pressure sensitive adhesive optical member. The gelfraction of the pressure sensitive adhesive layer was 58%.

Example 6

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount (solidscontent) of the acrylic polymer (B1) solution to be used was changed to0.1 part. Further, a pressure sensitive adhesive layer was formed in thesame manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 60%.

Example 7

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount (solidscontent) of the acrylic polymer (B1) solution to be used was changed to3 parts. Further, a pressure sensitive adhesive layer was formed in thesame manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 54%.

Comparative Example 1

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the acrylic polymer (B1)was not used. Further, an pressure sensitive adhesive layer was formedin the same manner as in Example 1 except that the above pressuresensitive adhesive composition was used, and also a pressure sensitiveadhesive optical member was obtained. The gel fraction of the pressuresensitive adhesive layer was 50%.

Comparative Example 2

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount (solidscontent) of the acrylic polymer (B1) solution to be used was changed to5 parts. Further, a pressure sensitive adhesive layer was formed in thesame manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 40%.

Comparative Example 3

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the silane coupling agentwas not used. Further, a pressure sensitive adhesive layer was formed inthe same manner as in Example 1 except that the above pressure sensitiveadhesive composition was used, and also a pressure sensitive adhesiveoptical member was obtained. The gel fraction of the pressure sensitiveadhesive layer was 45%.

Comparative Example 4

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the amount of3-glycidoxypropyltrimethoxysilane to be used was changed to 3 parts.Further, a pressure sensitive adhesive layer was formed in the samemanner as in Example 1 except that the above pressure sensitive adhesivecomposition was used, and also a pressure sensitive adhesive opticalmember was obtained. The gel fraction of the pressure sensitive adhesivelayer was 47%.

Comparative Example 5 Preparation of High-Molecular Weight AcrylicPolymer (A)

A solution of an acrylic polymer (A3) having a weight-average molecularweight of 850,000 was obtained in the same manner as in Example 1 exceptthat the amount of acrylic acid to be used was changed to 5 parts. Thecarboxylic acid equivalent of the acrylic polymer (A3) was 6.61×10⁻⁴equivalent/g.

(Preparation of Low-Molecular Weight Acrylic Polymer (B))

A solution of an acrylic polymer (B3) having a weight-average molecularweight of 850,000 was obtained in the same manner as in Example 1 exceptthat the amount of acrylic acid to be used was changed to 1 part. Thecarboxylic acid equivalent of the acrylic polymer (B3) was 1.45×01equivalent/g.

(Preparation of a Pressure Sensitive Adhesive Composition for OpticalMembers, and Formation of a Pressure Sensitive Adhesive Optical Member)

A pressure sensitive adhesive composition for optical members was formedin the same manner as in Example 1 except that the acrylic polymer (A3)was used in place of the acrylic polymer (A1), and the acrylic polymer(B3) was used in place of the acrylic polymer (B1). Further, a pressuresensitive adhesive layer was formed in the same manner as in Example 1except that the above pressure sensitive adhesive composition was used,and also a pressure sensitive adhesive optical member was obtained. Thegel fraction of the pressure sensitive adhesive layer was 52%.

The pressure sensitive adhesive optical members (polarizing plates)obtained in the Examples and the Comparative Examples were evaluated asfollows. The results are shown in Table 1.

(Adhesion)

The pressure sensitive adhesive optical member cut into a piece of 25 mmin width was attached to a non-alkali glass plate by rolling a 2 kg rollonce, and then treated in an autoclave at 50° C., 0.5 MPa, for 30minutes. Then, the sample was left under the conditions of 23° C. and50% RH for 3 hours, and then measured for its peel adhesion (initialadhesion: N/25 mm) at a peel angle of 90° at a peel rate of 300 mm/min.On the other hand, the sample was treated in the autoclave and then leftat 70° C. for 48 hours, further left at 23° C. under 50% RH for 3 hours,and measured for its peel adhesion (adhesion after treatment: N/25 mm)at a peel angle of 90° at a peel rate of 300 mm/min. The adhesion afterheat treatment is desirably not increased from the initial adhesion.

Separately, the sample was treated in the autoclave, then left at 90° C.for 300 hours, left at 23° C. under 50% RH for 3 hours, and thenmeasured for its peel adhesion (adhesion after treatment: N/25 mm) at apeel angle of 90° at a peel rate of 300 mm/min. Whether the adhesive andthe optical member remained or not on the glass plate was observed withnaked eyes, and evaluation was conducted under the following criteria:

o: The pressure sensitive adhesive and the optical member did not remainat all.

x: The pressure sensitive adhesive and the optical member remained.

(Durability)

The pressure sensitive adhesive optical member cut in a size of 12inches was attached to a non-alkali glass plate of 0.5 mm in thickness,treated in an autoclave at 50° C., 0.5 MPa, for 30 minutes and thenintroduced into an atmosphere at 60° C., 90% RH, for 500 hours.Thereafter, the pressure sensitive adhesive optical member was observedwith naked eyes and evaluated under the following criteria:

o: The optical member was not peeled and was free of dry spots.

x: The optical member was peeled and had dry spots.

(Discoloration)

The pressure sensitive adhesive optical members cut in a size of 12inches were attached to both sides of a non-alkali glass plate of 0.5 mmin thickness such that the absorption axes of the polarizing plates wereperpendicular to each other, and then treated in an autoclave at 50° C.,0.5 MPa, for 30 minutes, and then introduced into an atmosphere at 90°C. for 500 hours. Thereafter, the sample was examined for itsdiscoloration with naked eyes and evaluated under the followingcriteria:

o: There was no discoloration.

x: There was discoloration.

TABLE 1 Adhesion Left at 90° C. (N/25 mm) for 300 hours TreatmentAdhesion Residual A. Initial at 70° C. (N/25 mm) adhesive I. DURABILITYII. DISCOLORATION Example 1 3.6 4.0 5.4 ∘ ∘ ∘ Example 2 3.8 4.4 7.9 ∘ ∘∘ Example 3 3.4 3.5 7.2 ∘ ∘ ∘ Example 4 2.9 3.1 6.5 ∘ ∘ ∘ Example 5 2.83.4 10.3 ∘ ∘ ∘ Example 6 5.5 7.5 11.9 ∘ ∘ ∘ Example 7 4.2 4.3 11.3 ∘ ∘ ∘Comparative 6.6 10.3 18 x ∘ ∘ Example 1 Comparative 3.5 3.8 14 ∘ x ∘Example 2 Comparative 3.7 4.1 12.5 x x ∘ Example 3 Comparative 5.3 11.613.5 ∘ ∘ ∘ Example 4 Comparative 10.4 18.9 20 ∘ ∘ x Example 5

In the above results, the pressure sensitive adhesive optical member ofthe present invention shows a small difference between the initialadhesion and the adhesion after treatment at 70° C., indicating that theadhesion is not increased after attachment to the liquid crystal cell.Accordingly, the optical member placed under any of the treatmentconditions can be easily re-released with good re-releasability withoutany residual adhesive and without destroying the liquid crystal cell,and thus the liquid crystal cell can be reutilized. Further, thepressure sensitive adhesive optical member is durable in the sever testfor a long time, is excellent in relaxation of stress caused by adimensional change in the optical member (polarizing plate) and is freeof adverse influence (discoloration) in liquid crystal display. Further,the adhesion of the pressure sensitive adhesive optical member to theglass is prevented from increasing after storage at high temperaturesfor a long time, and after release, no adhesive remains on the glass.Accordingly, only the glass can be easily isolated, and the recycling ofthe glass can be improved. On the other hand, it could be confirmed thatwhen the pressure sensitive adhesive optical members in the ComparativeExamples are attempted at satisfying durability or solve discoloration,the adhesion thereof is increased to make re-release of the opticalmember difficult. When the pressure sensitive adhesive optical membersin the Comparative Examples are released after storage at hightemperatures for a long time, the adhesive readily remains on the glass.

1. A pressure sensitive adhesive layer for optical members, which isformed by crosslinking a pressure sensitive adhesive composition foroptical members, wherein said pressure sensitive adhesive compositionfor optical members comprises: 100 parts by weight of an acrylic polymer(A) having a weight-average molecular weight of 500,000 or more,containing at least 50 wt % alkyl (meth)acrylate having an alkyl groupwith 5 or more carbon atoms and 0.2 to 2 wt % unsaturated carboxylicacid as the monomer unit; 0.1 to 4 parts by weight of an acrylic polymer(B) having a weight-average molecular weight of 2,000 to 50,000,containing at least 70 wt % alkyl (meth)acrylate and 1 to 7 wt %unsaturated carboxylic acid as the monomer unit and having a highercarboxylic acid equivalent than that of the acrylic polymer (A); and0.01 to 1 part by weight of a silane coupling agent, and a crosslinkingagent.
 2. The pressure sensitive adhesive layer for optical membersaccording to claim 1, wherein the gel fraction of the crosslinkedpressure sensitive adhesive layer for optical members is 35 to 90% byweight.
 3. A pressure sensitive adhesive optical member comprising thepressure sensitive adhesive layer according to claim 1 formed on oneside or both sides of an optical member.
 4. An image display using atleast one pressure sensitive adhesive optical member according to claim3.
 5. The pressure sensitive adhesive layer for optical membersaccording to claim 1, wherein the acrylic polymer (B) is contained in anamount of 0.1 to 2 parts by weight relative to 100 parts by weight ofthe acrylic polymer (A).
 6. The pressure sensitive adhesive layer foroptical members according to claim 1, wherein the acrylic polymer (B) iscontained in an amount of 0.2 to 1 part by weight relative to 100 partsby weight of the acrylic polymer (A).
 7. The pressure sensitive adhesivelayer for optical members according to claim 1, wherein the acrylicpolymer (A) contains a hydroxy group-containing monomer as the monomerunit.
 8. The pressure sensitive adhesive layer for optical membersaccording to claim 1, wherein the crosslinking agent is contained in anamount of 0.01 to 5 parts by weight relative to 100 parts by weight ofthe acrylic polymer (A).
 9. The pressure sensitive adhesive layer foroptical members according to claim 1, wherein the amount of crosslinkingagent is 0.01 to 5 parts by weight per 100 parts by weight of acrylicpolymer (A).